You'll probably have to read a book. The design discipline, for all it's pretensions at least admits that 'Hello World' is a fallacy.
Visual design works by playing on emotions, perception and psychology. There is no simple reducible formula that governs what people find engaging and attractive.
I'd suggest starting with 'Universal Principles of Design', it's written in a very easy to digest manner, but isn't dumbed down. Then move on to 'Grid Systems in Graphic Design'.
These two should give you enough grounding to 'prettify' for simple projects.